The present invention relates to superconducting systems including superconductors, such as superconducting wires or cables, including those configured as superconducting magnets, and cooling systems to maintain the temperature of the superconductors below its critical temperature.
Superconductors are phases that exhibit extremely low (essentially zero) electrical resistance below their critical temperature and critical magnetic field. Superconducting wires and cables have been used in a variety of applications, predominantly in superconducting electromagnetic magnets in which a superconductor is wound into a coil. Superconducting magnets have been used in applications including, for example, devices used for nuclear magnetic resonance (NMR) spectroscopy, magnetic resonance imaging (MRI), superconducting magnetic energy storage (SMES) and magnetic mine sweeping, as disclosed in, for example, Superconducting Magnets, M. N. Wilson, Oxford University Press, New York, N.Y. (1983) and Case Studies in Superconducting Magnets, Y. Iwasa, Plenum Press, New York, N.Y. (1994).
Known superconductors must be cooled to be made superconducting.and must be kept cool to remain superconducting, for example, in most typical prior art systems in a bath of liquid helium is used for cooling. A typical superconducting systems such as a superconducting magnet system, will include a coil form (e.g. a mandrel or bobbin) around which is wrapped a number of windings of cable or wire constructed of superconducting materials. Typical superconducting materials employed for such systems include Type II superconductors as defined in J. K. Hulm and B. T. Matthias, Superconductor Material Science, edited by S. Foner and B. B. Schwartz, Plenum Press, New York, N.Y., 1981, pp.37-53 such as superconductors including Nb3Sn-, Nb3Al-, and V3Ga-based compounds, and typically employed superconductors typically have critical temperatures below about 80 K and more commonly below about 40 K or even below about 20 K. In addition, the systems typically include vessels, within which the superconducting elements are placed. Often these vessels also utilize a liquid coolant, for example liquid helium, for cooling and maintaining the superconducting elements below their critical temperature for operation. Such vessels are hereinafter referred to as cryostats.
Typical prior art superconducting cryostat systems are operated using an external source of refrigeration which provides cooling power either to make liquid helium or other liquid gases or cold gas mixtures around the superconductors. In many systems, the helium is typically first cooled and liquefied to below the critical temperature of the superconductors and then introduced to the system. But these systems have several disadvantages. One is that they must have the ability to vent helium gas from the cryostat as heat is removed by converting the liquid helium into a gas; otherwise, the systems would pose an explosion danger. This venting of helium requires the systems to have a ready source of supplemental helium during operation, and also entails a considerable waste of helium, which is relatively expensive.
Cooling arrangements for superconducting systems have been proposed that do not involve a net loss of cooling fluid, such as helium. U.S. Pat. No. 5,419,142 to Good discloses such a system useful for providing back-up cooling of a cryostat in the event of a loss of the main refrigeration system, for example due to a power failure. The system disclosed by Good includes an external source of helium gas in fluid communication with a cryostat apparatus, containing a superconducting magnet, via a connection line including a special two-directional valve.
Cooling arrangements for superconducting systems involving sealed cryostats, which contain an essentially constant mass of cooling fluid during operation, have also been disclosed. Taylor et al. describe such a system, including a floating-ring superconducting magnet apparatus which has an internal volume, containing the superconducting wires on a coil form, which can be pressurized with helium gas and permanently sealed (Taylor et al. xe2x80x9cCoils for the Superconducting Levitron,xe2x80x9d Proceedings of Symposium on Engineering Problems of Fusion Research, January, 1970; Taylor et al. xe2x80x9cThe Livermore Superconducting Levitronxe2x80x9d Proceedings of Symposium on Engineering Problems of Fusion Research, January, 1970). The helium gas can then be cooled to a temperature below the superconducting temperature for the superconducting components. In the system described by Taylor et al., however, the vessel containing the superconducting components includes both the superconducting wire and the coil form and comprises a highly stressed, internally pressurized shell, which shell would typically need to be constructed to have a relatively thick wall thickness and/or be formed from materials of construction that are extremely. strong, and typically very expensive, in order to withstand the coolant gas pressures required.
While the system disclosed by Good can reduce the waste of helium and can enhance operating safety and enable the system to function for a time in the event of a loss of external refrigeration, and while the systems described by Taylor et al. can provide a sealed, constant mass superconducting magnet cryostat, there is still a need in the art for simple and inexpensive cryostat systems including superconductors that can reduce the waste of cooling medium, provide increased economy, simplicity and portability, and increase operational safety and flexibility.
The current invention involves novel superconducting cryostat apparatuses and methods for cooling superconducting cryostat apparatuses. The superconducting apparatuses according to the invention include a self-contained supply of a coolant medium. The mass of the coolant medium contained in an apparatus is conserved during operation. Thus, the superconducting apparatuses provided according to the invention can essentially eliminate the loss of cooling medium during operation. The inventive superconducting apparatuses also can eliminate the need for sources of external cooling during operation. The inventive apparatuses can thus be constructed to have lower operation and construction costs than typical prior art superconducting systems. The novel superconducting apparatuses provided by the invention can also have enhanced simplicity of operation and enhanced portability compared to typical prior art superconducting systems. The superconducting apparatuses provided according to the invention can be supplied with a quantity of cooling medium in gaseous form and at room temperature that is subsequently cooled to below the critical superconducting temperature of the superconductors contained within the apparatus via indirect cooling prior to operation of the apparatus. In some embodiments, once an apparatus has been cooled via indirect cooling, there is no subsequent need for external cooling during operation of the apparatus.
In one aspect, a superconducting cryostat apparatus is provided comprising a vessel, and at least one superconducting component including at least one superconductor contained within the vessel. The apparatus further includes at least one sealable container that is separate from the vessel containing the superconducting component, and that is in thermal communication with the superconductor. The sealable container has an internal volume that is able to contain a coolant. The sealable container, when containing the coolant, is able to maintain the superconductor at a temperature not exceeding its critical temperature during operation of the apparatus.
In another embodiment, a superconducting apparatus comprising a vessel and at least one superconductor contained within the vessel is provided. The superconducting apparatus further includes a heat absorption system including at least one sealable container that is separate from the vessel containing the superconductor. The apparatus requires no external source of cooling during operation of the apparatus.
In another embodiment, a superconducting cryostat apparatus is provided. The apparatus includes at least one superconducting component including at least one superconductor. The apparatus further includes at least one sealable container that is coiled and that has an internal volume containing at least one superconducting component. The internal volume is able to contain a coolant. The sealable container, when containing the coolant, is able to maintain the superconductor at a temperature not exceeding its critical temperature during operation of the apparatus.
In yet another embodiment, a superconducting cryostat apparatus comprising at least one superconducting wire, cable, or ribbon is provided. The apparatus further includes a sealable container having an internal volume, containing the superconducting wire, cable, or ribbon, and further providing void space about the superconducting wire, cable, or ribbon able to contain a coolant. The container forms a conduit around the superconducting wire, cable or ribbon such that a cross-sectional plane perpendicular to a longitudinal axis of the container intersects the superconducting wire, cable, or ribbon at only a single point along its length.
In another embodiment, a superconducting cryostat apparatus comprising at least one superconducting wire, cable, or ribbon coiled to form a winding pack is provided. The winding pack has a minimum external cross-sectional dimension of a first value. The apparatus further includes a sealable container. The sealable container has a minimum internal cross-sectional dimension of a second value that is less than the first value. The sealable container also has an internal volume able to contain a coolant. The sealable container, when containing the coolant, is able to maintain the superconducting wire, cable, or ribbon at a temperature not exceeding its critical temperature during operation of the apparatus.
In yet another embodiment, a superconducting cryostat apparatus comprising at least one superconducting wire, cable, or ribbon is provided. The apparatus further includes a sealable container. The sealable container has an internal volume able to contain a coolant that has a maximum internal diameter not exceeding 3 inches. The sealable container, when containing the coolant, is able to maintain the superconducting wire, cable, or ribbon at a temperature not exceeding its critical temperature during operation of the apparatus.
In another aspect, the invention provides a series of methods. One embodiment involves a method comprising introducing a mass of gas into at least one sealable container that is contained within a superconducting cryostat apparatus that includes at least one superconductor. The container is separate from a vessel containing the superconductor, and the gas has a temperature exceeding a critical temperature of the superconductor. The method further includes sealing the container after introduction of the gas.
Another embodiment provides a method comprising providing at least one sealable container having an internal volume containing at least one superconducting component including at least one superconductor, where the sealable container is coiled. The method further includes introducing a mass of gas into the sealable container, where the gas has a temperature exceeding a critical temperature of the superconductor, and then sealing the container.